FROM THE PREFACE: Dramatic adjustments ensue within the body structure of such a lot animals in the course of their improvement. one of the vertebrates, birds are fullyyt oviparous, dwell for variable classes in a cleidoic egg, and convey primary adjustments in excretion, meals, and breathing on the time of hatching. against this, the eutherian mammals are all viviparous, rely on the maternal flow and a really expert placenta to supply nutrition, alternate gases, and discharge wastes.